I've worked in horse racing my entire life and have seen pretty much every type of condioner and tool out there.
For arenas, or any type of riding surface, your equipment is largely dependant on the surfance type.
For race tracks we have a few main tools. A condioner, harrows, rollers and floats
A condioner is a 3 phase tool. It scarifies, rolls and breaks up the soil and drag harrows. It's best for hard packed, etc... You can adjust the height and deepness to get a consistant surface.
A float is a steal I beam on the 3pt hitch. It's purpose is to float the water off the top and leave a flat surface so new water will roll off.
Drag harrows are a must for any operation. Although fixed harrows on wheels are nice, they don't follow the contour of the ground and cause incosistant depth.
Rollers are used for sealing the ground. If you are expecting rain but have an event the following day, it's best to seal the dirt. All new water rolls off of the top.
With our arena we are able to get by with just drag harrows. It's sandy enough that it only gets hard in the coldest of winter.
Watering is also key in maintaining a nice surface. Too much water you get a hard surface. Not enough and you get poor footing and dust.
There is also the option of chemicals. We use different chemicals depending on the surface and weather. Lime to keep tracks from freezing, etc.... However, they can be harmful to your horses feet if used in excess.
Also, a surface is only good for so many years. Eventually it reaches the point where it won't work up the same and will always be too hard or too deep.